Fixing an issue where reference count increases were not applied in certain cases

src/QsCompiler/QirGeneration/Context.cs

@@ -1099,7 +1099,7 @@ private Value ConditionalEvaluation(Value condition, Func<IValue>? onCondTrue =
                 throw new InvalidOperationException("a default value is required if either onCondTrue or onCondFalse is null");
             }
 
-            var defaultRequiresRefCount = increaseReferenceCount && defaultValue != null && this.ScopeMgr.RequiresReferenceCount(defaultValue.LlvmType);
+            var defaultRequiresRefCount = increaseReferenceCount && defaultValue != null && ScopeManager.RequiresReferenceCount(defaultValue.LlvmType);
             var requiresTrueBlock = onCondTrue != null || defaultRequiresRefCount;
             var requiresFalseBlock = onCondFalse != null || defaultRequiresRefCount;
 
@@ -1126,7 +1126,7 @@ IValue ProcessBlock(Func<IValue>? evaluate)
                 {
                     this.ScopeMgr.OpenScope();
                     var evaluated = evaluate?.Invoke() ?? defaultValue!;
-                    this.ScopeMgr.CloseScope(evaluated, false); // force that the ref count is increased within the branch
+                    this.ScopeMgr.CloseScope(evaluated); // forces that the ref count is increased within the branch
                     return evaluated;
                 }
                 else

src/QsCompiler/QirGeneration/Subtransformations/StatementKindTransformation.cs

@@ -289,14 +289,13 @@ public override QsStatementKind OnConditionalStatement(QsConditionalStatement st
                 this.SharedState.EndBranch();
             }
 
-            // Finally, set the continuation block as current or prune it if it is unused.
-            if (contBlockUsed)
+            // Finally, set the continuation block as current and prune it if it is unused.
+            this.SharedState.SetCurrentBlock(contBlock);
+            if (!contBlockUsed)
             {
-                this.SharedState.SetCurrentBlock(contBlock);
-            }
-            else
-            {
-                this.SharedState.CurrentFunction.BasicBlocks.Remove(contBlock);
+                // This is the savest option to deal with this case from a code rubustness perspective.
+                // The additional code blocks that don't have any predecessors are better trimmed in a separate pass over the generated ir.
+                this.OnFailStatement(SyntaxGenerator.StringLiteral("reached unreachable code...", ImmutableArray<TypedExpression>.Empty));
             }
             return QsStatementKind.EmptyStatement;
         }
@@ -417,7 +416,7 @@ public override QsStatementKind OnRepeatStatement(QsRepeatStatement stm)
                 // We need to make sure to properly invoke all calls to unreference, release, and remove alias counts
                 // for variables and values in the repeat-block after the statement ends.
                 this.SharedState.SetCurrentBlock(contBlock);
-                this.SharedState.ScopeMgr.ExitScope(false);
+                this.SharedState.ScopeMgr.ExitScope();
 
                 this.SharedState.SetCurrentBlock(fixupBlock);
                 this.Transformation.Statements.OnScope(stm.FixupBlock.Body);

src/QsCompiler/Tests.Compiler/QirTests.fs

@@ -77,7 +77,8 @@ let ``QIR inlined call`` () = qirTest true "TestInline"
 let ``QIR alias counts`` () = qirTest false "TestAliasCounts"
 
 [<Fact>]
-let ``QIR reference counts`` () = qirTest false "TestReferenceCounts"
+let ``QIR reference counts`` () =
+    qirMultiTest false "TestReferenceCounts" [ "TestReferenceCounts1"; "TestReferenceCounts2" ]
 
 [<Fact>]
 let ``QIR built-in functions`` () = qirTest false "TestBuiltIn"

src/QsCompiler/Tests.Compiler/TestCases/QirTests/TestBools.ll

@@ -12,4 +12,9 @@ then0__1:                                         ; preds = %entry
 
 else__1:                                          ; preds = %entry
   ret i1 %e
+
+continue__1:                                      ; No predecessors!
+  %1 = call %String* @__quantum__rt__string_create(i8* getelementptr inbounds ([28 x i8], [28 x i8]* @0, i32 0, i32 0))
+  call void @__quantum__rt__fail(%String* %1)
+  unreachable
 }

src/QsCompiler/Tests.Compiler/TestCases/QirTests/TestConditional1.ll

@@ -20,4 +20,11 @@ else__1:                                          ; preds = %entry
   call void @__quantum__rt__array_update_alias_count(%Array* %arg__1, i32 -1)
   call void @__quantum__rt__tuple_update_alias_count(%Tuple* %1, i32 -1)
   ret i64 0
+
+continue__1:                                      ; No predecessors!
+  %4 = call %String* @__quantum__rt__string_create(i8* getelementptr inbounds ([28 x i8], [28 x i8]* @6, i32 0, i32 0))
+  call void @__quantum__rt__array_update_alias_count(%Array* %arg__1, i32 -1)
+  call void @__quantum__rt__tuple_update_alias_count(%Tuple* %1, i32 -1)
+  call void @__quantum__rt__fail(%String* %4)
+  unreachable
 }

src/QsCompiler/Tests.Compiler/TestCases/QirTests/TestConditional3.ll

@@ -11,6 +11,11 @@ then0__2:                                         ; preds = %then0__1
 else__2:                                          ; preds = %then0__1
   ret i64 2
 
+continue__2:                                      ; No predecessors!
+  %0 = call %String* @__quantum__rt__string_create(i8* getelementptr inbounds ([28 x i8], [28 x i8]* @3, i32 0, i32 0))
+  call void @__quantum__rt__fail(%String* %0)
+  unreachable
+
 else__1:                                          ; preds = %entry
   br i1 %branch2, label %then0__3, label %else__3
 
@@ -19,4 +24,14 @@ then0__3:                                         ; preds = %else__1
 
 else__3:                                          ; preds = %else__1
   ret i64 4
+
+continue__3:                                      ; No predecessors!
+  %1 = call %String* @__quantum__rt__string_create(i8* getelementptr inbounds ([28 x i8], [28 x i8]* @4, i32 0, i32 0))
+  call void @__quantum__rt__fail(%String* %1)
+  unreachable
+
+continue__1:                                      ; No predecessors!
+  %2 = call %String* @__quantum__rt__string_create(i8* getelementptr inbounds ([28 x i8], [28 x i8]* @5, i32 0, i32 0))
+  call void @__quantum__rt__fail(%String* %2)
+  unreachable
 }

src/QsCompiler/Tests.Compiler/TestCases/QirTests/TestReferenceCounts.qs

@@ -3,6 +3,21 @@
 
 namespace Microsoft.Quantum.Testing.QIR {
 
+    newtype HasString = (
+        Value: String,
+        Data: Double[]
+    );
+
+    operation TestPendingRefCountIncreases(cond : Bool) : HasString {
+        let s = HasString("<", [0.0]);
+        let updated = s w/ Data <- [0.1, 0.2];
+        if cond {
+            return s;
+        } else {
+            return s;
+        }
+    }
+
     function TestRefCountsForItemUpdate(cond : Bool) : Unit {
         mutable ops = new Int[][5];
         if (cond) {

src/QsCompiler/Tests.Compiler/TestCases/QirTests/TestReferenceCounts2.ll

@@ -0,0 +1,68 @@
+define { %String*, %Array* }* @Microsoft__Quantum__Testing__QIR__TestPendingRefCountIncreases__body(i1 %cond) {
+entry:
+  %0 = call %String* @__quantum__rt__string_create(i8* getelementptr inbounds ([2 x i8], [2 x i8]* @0, i32 0, i32 0))
+  %1 = call %Array* @__quantum__rt__array_create_1d(i32 8, i64 1)
+  %2 = call i8* @__quantum__rt__array_get_element_ptr_1d(%Array* %1, i64 0)
+  %3 = bitcast i8* %2 to double*
+  store double 0.000000e+00, double* %3, align 8
+  %s = call { %String*, %Array* }* @Microsoft__Quantum__Testing__QIR__HasString__body(%String* %0, %Array* %1)
+  %4 = getelementptr inbounds { %String*, %Array* }, { %String*, %Array* }* %s, i32 0, i32 1
+  %5 = load %Array*, %Array** %4, align 8
+  call void @__quantum__rt__array_update_alias_count(%Array* %5, i32 1)
+  %6 = bitcast { %String*, %Array* }* %s to %Tuple*
+  call void @__quantum__rt__tuple_update_alias_count(%Tuple* %6, i32 1)
+  %7 = call %Tuple* @__quantum__rt__tuple_copy(%Tuple* %6, i1 false)
+  %updated = bitcast %Tuple* %7 to { %String*, %Array* }*
+  %8 = getelementptr inbounds { %String*, %Array* }, { %String*, %Array* }* %updated, i32 0, i32 1
+  %9 = call %Array* @__quantum__rt__array_create_1d(i32 8, i64 2)
+  %10 = call i8* @__quantum__rt__array_get_element_ptr_1d(%Array* %9, i64 0)
+  %11 = bitcast i8* %10 to double*
+  %12 = call i8* @__quantum__rt__array_get_element_ptr_1d(%Array* %9, i64 1)
+  %13 = bitcast i8* %12 to double*
+  store double 1.000000e-01, double* %11, align 8
+  store double 2.000000e-01, double* %13, align 8
+  store %Array* %9, %Array** %8, align 8
+  call void @__quantum__rt__array_update_alias_count(%Array* %9, i32 1)
+  call void @__quantum__rt__tuple_update_alias_count(%Tuple* %7, i32 1)
+  br i1 %cond, label %then0__1, label %else__1
+
+then0__1:                                         ; preds = %entry
+  call void @__quantum__rt__array_update_alias_count(%Array* %5, i32 -1)
+  call void @__quantum__rt__tuple_update_alias_count(%Tuple* %6, i32 -1)
+  call void @__quantum__rt__array_update_alias_count(%Array* %9, i32 -1)
+  call void @__quantum__rt__tuple_update_alias_count(%Tuple* %7, i32 -1)
+  call void @__quantum__rt__string_update_reference_count(%String* %0, i32 -1)
+  call void @__quantum__rt__array_update_reference_count(%Array* %1, i32 -1)
+  call void @__quantum__rt__array_update_reference_count(%Array* %9, i32 -1)
+  call void @__quantum__rt__tuple_update_reference_count(%Tuple* %7, i32 -1)
+  ret { %String*, %Array* }* %s
+
+else__1:                                          ; preds = %entry
+  call void @__quantum__rt__array_update_alias_count(%Array* %5, i32 -1)
+  call void @__quantum__rt__tuple_update_alias_count(%Tuple* %6, i32 -1)
+  call void @__quantum__rt__array_update_alias_count(%Array* %9, i32 -1)
+  call void @__quantum__rt__tuple_update_alias_count(%Tuple* %7, i32 -1)
+  call void @__quantum__rt__string_update_reference_count(%String* %0, i32 -1)
+  call void @__quantum__rt__array_update_reference_count(%Array* %1, i32 -1)
+  call void @__quantum__rt__array_update_reference_count(%Array* %9, i32 -1)
+  call void @__quantum__rt__tuple_update_reference_count(%Tuple* %7, i32 -1)
+  ret { %String*, %Array* }* %s
+
+continue__1:                                      ; No predecessors!
+  %14 = call %String* @__quantum__rt__string_create(i8* getelementptr inbounds ([28 x i8], [28 x i8]* @1, i32 0, i32 0))
+  %15 = getelementptr inbounds { %String*, %Array* }, { %String*, %Array* }* %s, i32 0, i32 0
+  %16 = load %String*, %String** %15, align 8
+  call void @__quantum__rt__array_update_alias_count(%Array* %5, i32 -1)
+  call void @__quantum__rt__tuple_update_alias_count(%Tuple* %6, i32 -1)
+  call void @__quantum__rt__array_update_alias_count(%Array* %9, i32 -1)
+  call void @__quantum__rt__tuple_update_alias_count(%Tuple* %7, i32 -1)
+  call void @__quantum__rt__string_update_reference_count(%String* %0, i32 -1)
+  call void @__quantum__rt__array_update_reference_count(%Array* %1, i32 -1)
+  call void @__quantum__rt__string_update_reference_count(%String* %16, i32 -1)
+  call void @__quantum__rt__array_update_reference_count(%Array* %5, i32 -1)
+  call void @__quantum__rt__tuple_update_reference_count(%Tuple* %6, i32 -1)
+  call void @__quantum__rt__array_update_reference_count(%Array* %9, i32 -1)
+  call void @__quantum__rt__tuple_update_reference_count(%Tuple* %7, i32 -1)
+  call void @__quantum__rt__fail(%String* %14)
+  unreachable
+}

src/QsCompiler/Tests.Compiler/Tests.Compiler.fsproj

@@ -250,7 +250,10 @@
     <Content Include="TestCases\QirTests\TestRange.qs">
       <CopyToOutputDirectory>Always</CopyToOutputDirectory>
     </Content>
-    <Content Include="TestCases\QirTests\TestReferenceCounts.ll">
+    <Content Include="TestCases\QirTests\TestReferenceCounts1.ll">
+      <CopyToOutputDirectory>Always</CopyToOutputDirectory>
+    </Content>
+    <Content Include="TestCases\QirTests\TestReferenceCounts2.ll">
       <CopyToOutputDirectory>Always</CopyToOutputDirectory>
     </Content>
     <Content Include="TestCases\QirTests\TestReferenceCounts.qs">